Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 110434 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1134 PM EST Sun Dec 10 2017 .SYNOPSIS... Snow showers are expected to linger across the higher terrain through Monday morning. An Arctic cold front will drop south across the area early Monday. This boundary could trigger a few snow squalls across the mountains and foothills with its passage. The next low pressure system will affect Maine and New Hampshire Tuesday and Wednesday with another round of wintry precipitation. Colder weather follows this system for the end of the work week. && .NEAR TERM /TONIGHT/... 1130PM UPDATE... Some clearer skies in the eastern part of the area have allowed temperatures to drop there a bit more than forecast. Have adjusted overnight temperatures to reflect this. Otherwise forecast largely on track. Cold front dropping in from the north will link up with some lake moisture and produce some light snow in northern New Hampshire overnight. 8PM UPDATE... Have made minor adjustments to hourly temperature and dewpoint forecast based on latest observations. Dewpoints this evening running a little higher than forecast so bumped these up a bit. No other significant changes were made here. 4PM UPDATE... Have updated the forecast to account for current snow shower activity and structure precipitation chances such that they are more graduated. Lake effect band is sending moisture into NH and even western ME. Accumulation should be limited to western/northern NH where an inch is possible overnight. ORIGINAL DISCUSSION... At 19z...a 984 millibar low was vicinity of Newfoundland. An Arctic boundary extended from the Gaspe Peninsula through the upper Great Lakes. As expected...the westerly trajectory to the lee of Lake Ontario and upslope flow has produced a good deal of cloudiness across the higher terrain...along with an area of snow showers producing some light accumulations. Downwind of the higher terrain we were seeing varying amounts of low clouds. For tonight...a shortwave impulse will approach from the Great Lakes late tonight. At the surface a weak wave will ripple eastward along the Arctic boundary and help drive it southward into the mountains after midnight. This should produce more organized snow showers for a time...along with the possibility of a brief snow squall with its passage. Elsewhere...skies will average partly cloudy overnight with the chance of a brief snow shower or flurry. Lows will range from the teens across the mountains to the 20s elsewhere. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... The shortwave and Arctic boundary exit the area by midday with any lingering snow showers or flurries coming to an end. Highs will be reached by midday with falling afternoon readings as the Arctic air deepens across the area. We`ll see a brief break late tomorrow into Monday night under weak ridging. However...clouds will rapidly thicken and lower after midnight in warm air advection ahead of the next disturbance. Expect we`ll see precipitation breakout over much of New Hampshire and southwest Maine during the predawn hours of Tuesday. The column will be cold enough to support all snow at the onset. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Main Concerns for Tuesday through Sunday... *Significant winter storm will bring additional snowfall to much of the area on Tuesday with possible mixing along the coast. This will impact rush hours on Tuesday. *An Arctic air mass filters in for mid week creating very cold wind chills. Blocking downstream over the Atlantic will keep deep troughing over the northeastern CONUS with the northern jet stream/main storm track overhead for the foreseeable future. It will become colder locally with time with 700MB temperatures in the teens by mid week. At its nadir (Thursday), the cold will translate to tens and teens for the mountains and 20s and 30s south for highs. Overnight lows will drop as the single digits north to lower teens south. A winter weather watch has been issued for Tuesday for all areas except the coast and Waldo County. Many GEFS/NAEFS/ECMWF ensemble members are in agreement that at least advisory level snows will be seen all the way to the Canadian border, with warning level criteria for much of southern and central NH and southwest Maine. NAEFS percentiles, standardized anomalies, and return intervals all indicate that this is an anomalously strong system in relation to geopotential height falls and u and v winds. The latest deterministic model runs generally develop a secondary low just along the NH/ME coast before curling it NNE into northern Aroostook (aka "The County"). This path will draw in a fair amount of warm air ahead of the cyclone and bring the coastal front farther inland; thus the exclusion of the coast in the watch. However, strong cold air damming will exist north of the front especially in the foothills and we could see some mixed precipitation along the interface. In general expect p-type to be mainly snow once the system really wraps up with a few hours of moderate to heavy snow. This system should move out quickly very late Tuesday with some additional accumulating snows in the slopes for Wednesday. Gusty NW winds will arrive in its wake ushering in Arctic air. Bitter windchill values are forecast north of the foothills bottoming near -25 F Thursday morning, and a wind chill advisory or warning may be needed. Another system may affect the region Friday/Saturday but currently it is dipping south of northern New England. In general, with cyclonic flow in place clouds and showers will remain in the extended forecast. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... Short Term...Areas of MVFR possible in snow showers north of the mountains with local IFR conditions through Monday morning. Elsewhere VFR is expected. MVFR will develop after 06z Tue and lower to IFR by the end of the period in snow. Long Term...A storm will impact the region on Tuesday. Expect IFR in snow starting early Tuesday morning and continuing through the day. Snow comes to an end late Tuesday night and conditions will return to VFR by Wednesday expect in the upslope mountain areas where MVFR SHSN will persist through Thursday. && .MARINE... Short Term...We`ll see one more surge of wind tonight into Monday with SCA conditions likely. We should briefly drop below SCA Monday night under weak ridging ahead of the next storm system. Long Term...A low will develop and cross the Gulf of Maine on Tuesday bringing precipitation. In its wake northwesterly flow will develop and strengthen to gale force by Wednesday night under cold advection. Gales will subside by Thursday morning but Small Craft advisories will persist through the end of the week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Watch from late Monday night through late Tuesday night for MEZ007>009-012>014-018>022. NH...Winter Storm Watch from late Monday night through late Tuesday night for NHZ001>013-015. MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ150>154. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Schwibs LONG TERM...Hanes

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